Author: szeloof

Prototype VLF/ELF Receiver Frontend Testing

Quick prototype of a VLF/ELF receiver with two stage low noise amplifier and passive RC bandpass filtering. First stage has a gain of 180 then is fed to a lowpass and highpass filter then to another opamp with adjustable gain up to 500. Resulting signal is sent to a Focusrite Scarlet i2i 24bit USB audio interface and sampled at 192KHz.

This simple preamplifier can easily pick out the “fire crackling” of lightning strikes around the world form the noise floor and can easily resolve other natural low frequency radio phenomena such as “”whistlers”. Active bandpass filtering and 60Hz notch filter will be added as well as a shielding enclosure and low noise Analog Devices OP270 or similar opamps will be used in another iteration of the design.

Antenna used was two large screw drivers inserted into the ground soil separated by about 50 feet in the woods 1/4 mile from any house or power lines. 60Hz noise was exceptionally low considering only passive RC filtering was used which has high and low -3dB points far away from what you actually design the cutoff frequencies of the filter to be.

This frontend contained no input protection in the form of glow discharge neon lamp, clamping diodes, thermistor, MOV, fuse, etc. Next design will incorporate multiple such devices however it is not a great priority for testing because I am using the screwdriver ground probes for antenna which is less susceptible to high voltage buildup in storms as a whip or dipole antenna.

http://www.vlf.it/

Sputtering Setup V2

I machined a delrin insulator with fiberglass center rod for the CF 4 pin electrical feedthrough to provide power to the two incandescent substrate heaters in my new sputtering setup and to allow for instrumentation hookup.

New sputtering setup has dual substrate heaters as well as insulated feedthroughs for both target and substrate so that it can operate in DC, RF, Bias sputtering modes, or any combination therein. A quartz microbalance thickness monitor will be added soon.

The second to last image shows multiple colors in glow discharge during sputtering possibly due to DC bias. Bottom and top electrodes are both at different potentials with respect to chamber ground, so it is possible that different gasses are ionized due to differences in ionization energies of the residual gaseous species.

Microwave Plasma Interferometer Prototyping

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Prototyping of a microwave interferometer setup has begun using modified police radar and satellite television parts, namely Gunn Diode oscillators (gunnplexer) and LNBs with dielectric resonant oscillators as well as PLL synthesized ones. Tests are being conducted at X, Ku, and K bands. The goal of this is to non-intrusively measure electron density in plasmas in my chamber. Results of these experiments will be posted.

Photonic Nanostructes in Butterfly Wings – SEM Analysis

Nano-scale features on butterfly wing scales interact with specific wavelengths of visible light (photonic bandgap material) to produce bright colors as observed by the human eye. This structure, for example, removes certain wavelengths from the white light that hits it (mainly blue, 472nm) so that the color, when observed by the human eye, appears orange.

SEM Sample Preparation – DC Sputtering

Thin films of copper were prepared on non-conductive samples to be observed under the Electron Microscope. This process is called DC Diode Sputtering and took place at just below 100mTorr and 2000v @ 150watts.

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This same setup can be used at lower powers to plasma clean or etch the top layer surface of the sample for better images under the SEM. Oxygen (and sometimes a small amount of Nitrogen) is usually a much more effective gas for this cleaning than Argon and leads to less unwanted sputtering as well.

Sputtering system v2 was made to support DC and RF sputtering so I can make dielectric coatings as well and it supports larger target and substrate samples. An insulator will be constructed to mount the target holder to the main chamber walls so that RF can be used more effectively.

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SEM Demo

ICP Extraction and Plasma Cleaning

A simple Inductively Coupled Ion Source can be made by using a negative bias on an extractor cone or electrode to attract the positive ions and can later be focused into a beam with magnets. Such a source is suitable at high powers as a Deuteron source for an IEC fusor or for processes such as ion beam deposition or directional plasma cleaning. As seen in Patent #4,793,961, these architectures have been proven for exceptional use as hydrogen or deuterium ion sources.

The ICP coil is placed on a quartz tube mounted via a Kovar KF40 flange to the vacuum chamber and an antenna tuner (matching network) is used to couple the RF energy from 10 meter Ham radio transmitter to the coil. A Multi-cusp Magnetic assembly could be used as shown below to keep energetic electrons from being lost into the ion source walls, confine their motion, and reduce the occurrence of electron-ion recombination.

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A high (low) negative voltage (usually between -400v and -2kv) is used on the extractor electrode. If this design was implemented in an IEC fusor, the extractor could be grounded because the fusor grid is held at a negative potential.

Fluorescence was observed in the quartz tube during these experiments due to electron bombardment. While the chamber was pumped down and MFCs setup, a DC copper sputtering environment was created for testing purposes as well as a controlled and isolated anode glow region of an incomplete glow discharge which forms a spherical region above the copper plate (anode) and could be used for uniform plasma cleaning.

Garage Electron Microscopy – First Images

A huge thanks to David Bono from the DMSE UGTL lab at MIT for training me in basic SEM operation during a recent college visit on MIT’s JEOL JSM-6400, which is very similar to my JSM-6300. Because of David Bono and Colin Marcus’s generosity I was able to get my SEM up and running.

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Miscellaneous Vacuum Chamber Upgrades

Miscellaneous Upgrades – Vent Valve/TC Gauge CF Tee Construction, Gas Cylinder Holder Fabrication, and Ion Gauge Controller Analog Output Hack

My HP (Granville Phillips)  hot cathode ionization gauge controller (59822b) had provisions for an analog output however the optional connector was not installed on the back panel and the connection points on the main PCB of the controller did not show any voltage deflection proportional to pressure so I took the pressure output from one of the stages in the electrometer which happened to be one of the outputs of a quad opamp chip. This output is fed to a NI DAQ USB6009 and displayed in a LabView VI so that the pressure of the chamber while pumping down can be held constant when requested by PID feedback loop with one or more of the mass flow controllers.

A pressurized gas cylinder holder was designed and fabricated by Diversatech Manufacturing, INC (www.diversatech.com) for safer operation of my vacuum chamber when using gasses such as Oxygen, Nitrogen, or Argon for processes such as sputtering or plasma cleaning.

 

ICP Residual Gas Color Analysis

Due to different gasses pumping out of chambers at different rates (i.e. Hydrogen always has a low pumping speed) and air’s natural composition changing glow discharge colors can be observed while pumping down a vacuum chamber. This was an attempt to estimate the pressure of the chamber indirectly during a pump down by observing and analyzing the inductively coupled plasma color at constant RF voltage.